In the commercial production of non-woven fabrics from a batt of random, loose, ultrasonically fusible fibers, after formation the batt is passed between a plurality of staggered horns of an ultrasonic welding machine, between the horns and an anvil roller having a pattern of projections formed thereon. Typical conventional apparatus is disclosed in copending application Ser. No. 290,714 filed Aug. 6, 1981 now U.S. Pat. No. 4,394,208 (the disclosure of which is hereby incorporated by reference herein), and copending application Ser. No. 145,833 filed May 1, 1980 now U.S. Pat. No. 4,311,540 (the disclosure of which is hereby incorporated by reference herein). By providing the proper pattern, spacing, and size of the projections on the anvil roller, it is possible to obtain a non-woven fabric that has a textile-like hand and drape, with high tensile strength, elongation, and tear strength properties. A high density and large number of primary bond points are uniformly distributed over the entire surface of the web, with each individual bond point maintained at the smallest practical size so that the total percentage of primary-bonded area of the fabric is maintained low.
Each ultrasonic power unit emits a certain amount of ultrasonic vibration energy to the web. This energy absorption is time dependent in the sense that the total power must be distributed to the entire surface of the web. For a given density of welding area, such as 10% of the total surface area, increasing the process speed draws higher and higher power until the maximum safe continuous power capability is reached for the particular unit. With this power limitation, one can either vary the speed or the density of welding. At the maximum power setting, increasing the speed of the process by two fold will require decreasing the density of the weld area by 50%, say from a 10% surface area to a 5% surface area of welding.
While the practice of such conventional procedures results in the production of a desirable non-woven fabric, the necessity of providing a high density of bond points each with the smallest practical size makes it extremely difficult to achieve high production speeds. For instance, typical production speeds are within the range of 10-30 meters/minute. When high speed commercially available batt formation equipment is utilized to form the batt of random, loose, ultrasonically fusible fibers, the speed of production of the non-woven fabric is limited by the speed of the ultrasonic bonding equipment, the batt-formation apparatus being capable of forming a suitable batt at a much higher speed than 50 meters/minute.
According to the present invention, a method and apparatus are provided that overcome the speed limitations inherent in conventional production of non-woven webs with ultrasonic bonding equipment. According to the present invention, it is possible to form non-woven fabric with suitable textile-like hand and drape, and with high tensile strength, elongation, and tear strength properties at high speed (e.g. greater than 50 meters/minute), so that the ultrasonic bonding equipment is not a limiting apparatus in the production of non-woven fabric ultrasonically. This is accomplished, according to the present invention, primarily by providing a plurality (e.g. 3) of ultrasonic welding machines in series, spaced from each other in the feed direction of the batt. Each welding machine effects bonding of only a portion of the primary bonds formed in the fabric, therefore the limitations inherent in utilization of high density bonding equipment are avoided, with resultant increase in fabric production speed.
According to one aspect of the present invention, a method of producing a non-woven fabric from a batt of random, loose, ultrasonically fusible fibers is provided, the fabric having a predetermined number of primary bonding points per unit area formed with a plurality of ultrasonic welding machines, each machine spaced from each other in a batt feed direction. The method steps are:
(a) Feeding the batt fibers in a batt feed direction into operative engagement, in turn, with each of the ultrasonic welding machines. PA1 (b) Supplying energy to each of the ultrasonic welding machines to effect formation of primary bonding points therewith. And, (c) effecting bonding of substantially less than all of the predetermined number of primary bonding points with each of the ultrasonic welding machines, but so that together the machines provide all of the predetermined number of bonding points desired. The number of ultrasonic welding machines provided is "x", wherein "x" is a positive integer greater than one; and preferably step (c) is practiced so that each of the machines bonds approximately (n/x) primary bonding points, wherein "n" is the predetermined desired number of bonding points per unit area. Thus where three ultrasonic welding machines are provided, each machine preferably effects bonding of about one-third of the primary bonding points. Preferably each of the machines applies a pattern of primary bonds (e.g. a straight-line pattern, or a helical pattern) to the batt that is the same as the pattern applied by the other machines, with each pattern offset from the other pattern in a dimension perpendicular to the batt feed direction.
According to another aspect of the present invention, apparatus for effecting the formation of a non-woven fabric is provided. The apparatus includes a plurality of ultrasonic welding machines, each machine including a set of horns and an anvil roller. Means are provided for mounting the welding machines so that they are spaced from each other in a direction of batt feed so that the batt may pass between the horns and anvil of each machine. Means are provided for transporting the batt in the feed direction between the horns and anvil of each of the machines; and means are provided for supplying energy, to effect ultrasonic bonding, to each of the machines at the same time. Preferably each of the anvil rollers has Y raised projections formed thereon, in a particular pattern, and the non-woven fabric produced has approximately "n" primary bonding points per unit area, wherein "n" is a positive integer evenly divisible by Y. The relationship (n/Y)=x is approximately true, each machine effecting bonding of a proportional number of the bonding points.
Utilizing the apparatus described above, it is possible to obtain suitable non-woven fabric production without providing any special configuration of the horns (such as in U.S. Pat. No. 4,146,416 or German Off. 22 59 203), and without requiring special equipment for staggering a plurality of horns associated with each anvil roller (such as in U.S. Pat. No. 3,733,238). This provides for much simpler apparatus for mounting of the horns, and easier access for replacement, repair, or the like thereof. Utilizing the apparatus according to the invention, the horns of each of the welding machines may be placed in-line with each other and spaced from each other a small distance in a dimension substantially transverse to the batt feed direction. The horns of at least one of the machines are staggered along the dimension substantially transverse to the feed direction with respect to the horns of at least one of the other machines, so that essentially every portion of the batt across the width thereof passes in operative association with at least one horn of at least one of the ultrasonic welding machines.
It is the primary object of the present invention to provide for the ultrasonic high speed production of suitable non-woven fabric. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.